全文获取类型
收费全文 | 177篇 |
免费 | 8篇 |
专业分类
林业 | 92篇 |
农学 | 4篇 |
36篇 | |
综合类 | 3篇 |
农作物 | 4篇 |
水产渔业 | 13篇 |
畜牧兽医 | 26篇 |
园艺 | 5篇 |
植物保护 | 2篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 14篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 5篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有185条查询结果,搜索用时 750 毫秒
91.
Olli Venelampi Assi Weber Timo Rönkkö Merja Itävaara 《Compost science & utilization》2013,21(3):200-209
The compostability of several paper products was determined according to the standards and criteria of the European standardization committee (CEN). The lignin content of the materials seems to be the main reason for the low biodegradability level achieved in the controlled composting test, which is a biodegradability test based on microbial degradation and measurement of carbon dioxide evolution. Mechanically pulped paper, which contains more lignin and more closely resembles natural wood than chemically bleached paper, generated smaller amounts of carbon dioxide. All the chemically bleached papers generated more than 70% of their organic carbon content as CO2, while the mechanically pulped unbleached papers in general generated less than 70%. Paper containing mechanical pulp degrades slower because lignin both interferes the biodegradation of cellulose and becomes incorporated in the humus. The test protocol also defines that, even if the biodegradability of paper products is not tested, their disintegration and effect on compost quality have to be determined. In the present study, we also evaluated a number of disintegration test methods in full-scale composting facilities. According to CEN, the disintegration can be studied either in composter bin-scale test equipment or in full-scale composting facilities. In this study, we only present the data from full-scale composting in which several test methods were used to evaluate the degradation of the samples. The disintegration of the paper products in full-scale composting facilities is highly dependent on the method used. The slowest degradation rate was achieved when the samples were composted in nylon bags. 相似文献
92.
Mating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in groups, but the actual mating system of this species, like many other group‐spawning fishes, has not been described in detail. Vendace typically spawn in the littoral or sublittoral zones of lakes in late autumn, and the hatching of larvae occurs close to icebreak in the following spring. In our large study lake, vendace larvae were caught in 93% of 1,149 random sampling locations lake‐wide. We examined the courtship and mating of vendace under experimental conditions by nonintrusive observation of the natural behaviour, to clarify whether spawning activity is associated with illumination and to assess the postspawning mortality of vendace. Here, we describe and document in detail for the first time the spawning behaviour of vendace: they spawn in the dark, and females release a small portion of their eggs (on average 1% of mean total individual fecundity) when the female and male, side by side, dart from near the bottom up towards the surface, that is perform a spawning rise. Males and females had several spawning rises (on average 1,200). Our results showed high postspawning mortality (56%). The spawning stress seems to be a potential component of mortality regulating the lifespan duration of vendace. 相似文献
93.
Pinus sylvestris-dominated forests have been heavily utilized across all of boreal Fennoscandia and the remaining natural forests are generally highly fragmented. However, there are considerable local and regional differences in the intensity and duration of past forest utilization. We studied the impact of human forest use on the diversity of epiphytic and epixylic lichens in late-successional Pinus sylvestris-dominated forests by assessing species richness and composition along both local and regional gradients in forest utilization. The effects of local logging intensity were analysed by comparing three types of stands: (i) near-natural, (ii) selectively logged (in the early 20th century) and (iii) managed stands. The effects of regional differences in duration and intensity of past forest use were analysed by comparing stands in two contrasting regions (Häme and Kuhmo–Viena). The species richness of selectively logged stands was as high as that of near-natural stands and significantly higher in these two stand categories than in managed stands. Species richness increased with the density of small understorey Picea, which correlated strongly with decreasing intensity of local forest use and increasing structural complexity of selectively logged and near-natural stands. Stands in the Häme region hosted a lower number of species, and were less likely to host many old-growth indicator species than the Kuhmo–Viena region, suggesting that species have been lost from stands in the Häme region due to a longer history of intensive forest use. We conclude that selectively logged stands, along with near-natural stands, are valuable lichen habitats particularly for species confined to old-growth structures such as coarse trees and deadwood. In landscapes where natural forests have become fragmented, the management or restoration of the remaining late-successional Pinus-dominated forests, e.g. through the use of fire, should be carefully planned to avoid adverse effects on lichen species richness. 相似文献
94.
Markus Holopainen Mikko Vastaranta Jussi Rasinmäki Jouni Kalliovirta Antti Mäkinen Reija Haapanen Timo Melkas Xiaowei Yu Juha Hyyppä 《European Journal of Forest Research》2010,129(6):1131-1142
Uncertainty factors related to inventory methodologies and forest-planning simulation computings in the estimation of logging
outturn assortment volumes and values were examined. The uncertainty factors investigated were (1) forest inventory errors,
(2) errors in generated stem distribution, (3) effects of generated stem distribution errors on the simulation of thinnings
and (iv) errors related to the prediction of stem form and simulation of bucking. Regarding inventory errors, standwise field
inventory (SWFI) was compared with area-based airborne laser scanning (ALS) and aerial photography inventorying. Our research
area, Evo, is located in southern Finland. In all, 31 logging sites (12 clear-cutting and 19 thinning sites) measured by logging
machine in winter 2008 were used as field reference data. The results showed that the most significant source of error in
the prediction of clear-cutting assortment outturns was inventory error. Errors related to stem-form prediction and simulated
bucking as well as generation of stem distributions also cause uncertainty. The bias and root-mean-squared error (RMSE) of
inventory errors varied between −11.4 and 21.6 m3/ha and 6.8 and 40.5 m3/ha, respectively, depending on the assortment and inventory methodology. The effect of forest inventory errors on the value
of logging outturn in clear-cuttings was 29.1% (SWFI) and 24.7% (ALS). The respective RMSE values related to thinnings were
41.1 and 42%. The generation of stem distribution series using mean characteristics led to an RMSE of 1.3 to 2.7 m3/ha and a bias of −1.2 to 0.6 m3/ha in the volume of all assortments. Prediction of stem form and simulation of bucking led to a relative bias of −0.28 to
0.00 m3 in predicted sawtimber volume. Errors related to pulpwood volumes were −0.4 m3 to 0.21 m3. 相似文献
95.
The neighbouring countries, Finland and Sweden, compete in the same market with their aquaculture. Both countries have had, until recently, stringent environmental policies limiting production volumes. During recent years, however, Swedish fish farmers have been able to increase their production volume, and Finnish fish farmers have also redirected their investments to Sweden. Thus, the strict Finnish environmental permit policy has not benefited the Baltic Sea environment, but has moved the production volumes and employment opportunities to other locations in the Baltic Sea and its drainage basin. By comparing the Finnish and Swedish fish farming governance systems, we found that in Sweden, various types of formal and informal interaction and practice have enhanced the achievement of balanced decisions. This has only rarely been the case in Finland, which features a more authoritative decision-making culture. On the other hand, increased communication across the Finnish administrative sectors raises future prospects for more holistic fish farming governance, which balances economic, social and environmental goals. 相似文献
96.
This paper analyses the major determinants of long‐ and short‐run labour productivity evolution for Chinese provinces between 1978 and 2010. The role played by openness to trade and foreign direct investment (FDI) constitutes the main focus of this analysis. From a methodological perspective, our main contribution is the inclusion of spatial effects into a dynamic error correction modelling framework. The results show that, in addition to domestic factors such as investment intensity and infrastructure use, trade openness and inward FDI also exert a direct impact on labour productivity. Furthermore, the geographical environment has a strong indirect influence on productivity: The more a region is surrounded by high‐productive regions with good infrastructure and linkages to the world economy, the higher are its productivity level and growth rate. The magnitude of these impacts varies by spatial regime (coastal, interior provinces) and time period in focus. Especially in the recent past, trade and FDI activity appear to be increasingly important drivers of regional productivity evolution, both for coastal and interior regions. These findings have important policy implications: In order to fully exploit the benefits from such spillovers, coordinated industrial policies which foster regional complementarities and support the free movement of production factors across regional borders are crucial. 相似文献
97.
Assessment of genetic structure,habitat suitability and effectiveness of reserves for future conservation planning of the Euphrates soft‐shelled turtle Rafetus euphraticus (Daudin, 1802)
下载免费PDF全文
![点击此处可从《水产资源保护:海洋与淡水生态系统》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Flora Ihlow Faraham Ahmadzadeh Hanyeh Ghaffari Ertan Taşkavak Timo Hartmann Claudia Etzbauer Dennis Rödder 《水产资源保护:海洋与淡水生态系统》2014,24(6):831-840
- 相似文献
98.
Integrated use of GIS,remote sensing and multi-criteria decision analysis to assess ecological land suitability in multi-functional forestry 总被引:1,自引:0,他引:1
The Zagros forests are a treasure of valuable oak forests, but they have been severely degraded from long-term misuse. Geographic information systems (GIS) and multi-criteria decision analysis (MCDA) have been increasingly used to improve the management of vulnerable ecosystems to prevent further degradation and increase the sustainability of land use. This study presents a methodology to assess land suitability using remote sensing (RS) to obtain wall-to-wall data for the calculations, GIS to analyze the data, and MCDA to rank alternative land uses. The criteria and subcriteria affecting the suitability of land for different uses were identified and weighted using an analytic hierarchy process. Variables used as subcriteria were assessed using satellite data and other sources of information such as existing maps and field surveys. Numerical values for the subcriteria were classified, and each class was given a priority rating according to expert judgments. Based on the ratings and weights of the subcriteria, a priority map was created for each land use using the weighted linear combination method. The priority maps for different land uses were overlaid to obtain a preliminary land use map, which often indicated several simultaneous land uses for the same location. The preliminary map was further edited by removing unrealistic, mutually exclusive land-use combinations. The study tested and demonstrated the potential of integrating RS, GIS and MCDA techniques for solving complicated land allocation problems in forested regions using a scientifically sound and practical approach for efficient and sustainable allocation of forestland for different uses. 相似文献
99.
100.
A species introduction experiment including several tropical pines and eucalypts was established in 1966/1967 in the Tchianga research station in Angolan Highlands. Despite 27 years of political conflict (1975-2002) and lack of management, the research experiment has remained relatively well conserved. We measured the best conserved plots that were 41 years old in 2007 to obtain information on the growth of different pine species. We calculated stand characteristics including basal area, dominant height, mean diameter, and stand volume for Pinus patula Schiede ex Schiltdl. Et Cham., Pinus pseudostrobus Lindl., Pinus kesiya Royle ex Gordon, Pinus devoniana Lindl., Pinus chiapensis (Martinez) Andresen, Pinus elliottii Engelm., Pinus greggii Engelm. Ex Parl., Pinus montezumae Lamb. and Pinus oocarpa Schiede ex Schltdl. The growing stock volume at 41 years was the highest in P. pseudostrobus, 1,325 m3·ha-1, followed by P. kesiya with 1,200 m3·ha-1. The widely planted P. patula had a growing stock volume of 892 m3·ha-1. P. oocarpa and P. pseudostrobus had the highest stand basal area, over 80 m2·ha-1. Using increment core analyses we studied the temporal development of stand characteristics. Analysis of the mean annual increment (MAI) showed that rotation lengths of 20-30 years would maximize wood production. With these rotation lengths, the MAI of P. pseudostrobus would be 35 m3·ha-1. Other productive species were P. kesiya, P. oocarpa and P. chiapensis. P. patula had a maximum MAI of 20 m3·ha-1. P. greggii had the lowest mean annual volume production, only about 13 m3·ha-1. 相似文献